This invention concerns reinforced concrete compositions. In particular, the invention concerns the use of nylon-4 reinforcing bars in wet-laid concrete compositions.
Concrete is a mixture of broken stone, gravel, cinders or slag, called "course aggregate", and sand or stone screenings, known as "fine aggregate" or "fines", with a cementing material, such as Portland cement. Concrete, reinforced by steel bars, is one of the most useful and important structural materials. Its attractiveness lies in its greater durability, requiring less maintenance; and the ease with which it is molded into shapes.
Reinforcing bars are usually constructed from steel and generally vary from about 0.25 to 1.5 inches in diameter. Round bars and more common; however, square bars are available. Steel reinforcing bars, nonetheless, present some problems. For example, steel bars are relatively rigid and are not easily adapted to irregular forms. They can also be relatively heavy and cumbersome to manipulate and position.
This invention is, in part, based upon the discovery that by substituting reinforcing bars constructed from nylon-4 for some or all of the steel reinforcing bars, the unique water-absorptive character of nylon-4 can be used to pre-stress the concrete, vastly improving its flexural strength.
Pre-stressing is achieved by embedding either wet or dry nylon-4 bars in a wet-laid concrete. The nylon-4 bars swell due to absorption of water, and consequently, as the concrete cures, the nylon-4 bars simultaneously shrink. The shrinkage of the bars pre-stresses the final concrete product, giving it significantly improved flexural strength.
The water-absorptive character of nylon-4 is well known. For example, U.S. Pat. No. 3,686,066, granted Aug. 22, 1972, to Peters describes shaped articles prepared by swelling nylon-4 with water and drying the swollen mass under pressure. While this characteristic has been used to prepare several articles, such as the humidity-responsive device described in U.S. Pat. No. 3,763,338, granted Oct. 2, 1973, to Tozer, it has not been used as reinforcing in concrete structures.